Analysis of the nonstability states during bending processes of metallic tubes at bending machines. P. 1, Derivation of the basic expressions and relationships

In this paper the derivation of expressions for admissible values of strains and stresses for vertex points of layers subjected to tension during tube bending at bending machines is presented. The conditions of the dispersed and located loss of stability of the bent tube and the cracking criterion based on the technological index A5 (five fold sample) were assumed as criteria of instability. The original element of this paper is the extension of the criterion of strain location in a form of possible initiation of a neck or furrow (introduced by Marciniak for thin plates [1]) to bending thin- and thick-walled metal tubes at bending machines. Occurrence of loss of stability (especially that in a localised form) during tube bending can strongly reduce the service life. Thus, it is recommended to avoid such states during tube bending for elbows for pipelines or pipe installations.

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Opracowanie ze środków MNiSW w ramach umowy 812/P-DUN/2016 na działalność upowszechniającą naukę.